By Joan Murray

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POMPANO BEACH (CBSMiami) — Fire investigators are still trying to figure out what caused a fierce blaze that claimed the lives of two little girls in Pompano Beach over the weekend.

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Monday, candles, flowers and stuffed animals are placed next to pictures of five-month-old Abigail Espinoza and her 5-year-old sister Sofia Melendez outside of the Banyan Club apartment that went up in flames Saturday just after 9 a.m.

Firefighters found the girls deceased in a bedroom.

“Not one alarm went off,” said Celia Delacruz who is friends with their mother.

Delacruz says she smelled smoke and feared for the children inside.

Investigators say the mother of the girls, 23-year-old Jocelyn Melendez went to work and left her 15-year-old sister to babysit all of her children.

The 15-year-old took Melendez’s two-year-old son with her to buy milk at the store, leaving the two girls alone in the apartment, according to Delacruz.

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But it is not clear how the fire started.

“We broke the windows with a fire extinguisher and we tried to yell to see if there were kids,” says a man who tried to help.

By the time firefighters arrived, it was too late.

The Medical Examiner says the autopsy results on the two children are pending.

The complex says the smoke alarms were working.

Investigators will determine if that is accurate.

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A shelter hearing is scheduled in Broward court Tuesday afternoon to determine where Melendez’s two-year-old son will stay.